Mikuni Oriko was the leader of the Southern Group and prior to that enemy to the Tomoe Mami and Sakura Kyouko by association.

Daughter of a ruined and corrupt politician she spent the time directly after contracting tracking down and exposing her father's associates. Her focus of vengeance soon expanded to criminals of all sorts and perpetrator of the smallest misdemeanour, slipping further into insanity, albeit keeping some semblance of grip in contrast to her later associates.

That was the time she started working together with Kure Kirika in targeting Mami and Kyouko and making their life hell. Always prodding their territory, poaching, so to speak. Soon after Miroko Mikuru and Hinata Aina joined the two, forming the Southern Group and thus escalating the conflict with the Mitakihara Four.

She introduced Chitose Yuma, newly contracted, as a fifth member into the group and mentored her.

Of the four of the original group, Mikuni Oriko was the sanest, which is not as hard as it may seem, and also the mastermind behind the groups formation and operation. In this role she was the James Moriarity befitting of Akemi Homura's Sherlock Holmes. The somewhat random incursions grew concerted, as did the killings of magical girls, which only stopped with the still mysterious near wipe-out of the Southern Group at the hands of demons.

As an historical figure she is rather ambiguous – especially considering her power. It is questionable if all of her actions were truly random and unjustified murder of innocent people or of she mayhaps used her power to weed out detrimental futures. Especially the recruitment of Yuma, not really matching the derange psychological make-up of the rest of the group, makes on wonder for Oriko's reasoning.

Her influence was notable of such an degree the Incubators regretted Oriko's recruitment.

She was able to transmit her prescient knowledge telepathically, greatly increasing the combat effectiveness of her group. It is assumed she was the most powerful precog of her generation, and incidentally also the last. Even then, when she was at the brink of her own death, she could only perceive darkness when trying to pierce the veil of death.